A.C. intermittant - im baffled

[bojangles]

my ac is good and cold sometimes... blows clouds into the car even.but then it goes weak.

the compressor is mostly running..is does seem to cut off once in a while.. sight glas shows a fairly consistant amount of bubbles..

no vacuum leaks the pump runs for about 8 secs when i switch on the key and then stops for more than a minute before kicking on for a few secs..

I Had the system drained and vacuumed dry.. it has 1.2 pounds of R134a in it.. we added dye to try and catch a small leak if it is there. then charged it with 2.2 pounds as per the service manual.
it is exactly the same..

Any suggestions?
S4s
Bruce

[flowers]

Hi,

Similiar situaiton to my S4s. Was down to 1.8 and recharged to 2.2 lbs. Now it is not as cold and compressor keeps cutting out. Checked voltage at low pressure switch on dryer and found switch is cutting in and out. Will be replacing both switch and drier this Saturday.

Rich Flowers
'95 S4s ...SHF63000 (with R-134A)
'79 JPS #040

[lotusguy]

Hi,

As mentioned, your pressure switch is suspect. Try jumping the switch circuit by making/installing a jumper wire w/ a male spade connector at each end and drive the car a couple of days and see if the issue doesn't go away. If so, it's time to replace the pressure switch. Happy Motoring! ...Jim'85TE

[bojangles]

it also seems temp related..in the morning the system seems to blow cold.. then as it warms it gets worse.

I see there is some control on the expansion valve.. what does that do?
I'll put a jumper on the low pressure switch at lunch and see what happens...

Today when i got to work, the compressor was running the air was cold yet the sight glass showed almost nothing.... usually it is a big smear.. I thought a fully charged system would have no bubbles but...

[bojangles]

i am suspicious that something is closing the expansion valve... this shuts the flow of refrigerant down then causes the low pressure side to drop lower due to suction of the compressor and then the switch cuts the compressor off...

what do you think?

[lotusguy]

bojangles said:

i am suspicious that something is closing the expansion valve... this shuts the flow of refrigerant down then causes the low pressure side to drop lower due to suction of the compressor and then the switch cuts the compressor off... what do you think?

Hi,

You don't want to start messing with the expansion valve. This valve uses a combination of line pressure and temp reading from a thermistor to regulate the refrigerant flow to both keep the evaporator from freezing as well as preventing liquid refrigerant from returning to the compressor (very Bad!). It would require special diagnostic tools to readjust it properly. This is something you don't want to mess up unless you already have a replacement compressor sitting on your work bench .

It is however a valve and so is subject to failing and clogging. First thing is to be sure the thermistor tip is not obstructed or covered. If it isn't or fixing that problem results in 'No-Joy', then you're probably looking at replacement. Happy Motoring! ...Jim'85TE

[Autocross7]

Not sure I can add anything constructive here... but I'm not sure I think the sight glass on these cars is worth a dime. Mine always has bubbles... even when properly charged. Car blows cold, pressure in the low pressure side is correct, pressur on the high pressure side is correct.... site glass ignored!

Drive topless!!!
Cameron

[bojangles]

with the black tape there it is hard to make heads or tails of it
there is a thermocouple that is connected to the system too.. i wonder if it is shutting things down when i drive...
i think i need a light on the compressor wire to see if it is shutting down when i drive..

maybe free-scan is needed...
something is shutting it off.. i jumpered the pressure switch on the way home today and it was better but still cycled on and off.

[black]

For what its worth, I had the same problem. I needed a new dryer and expansion valve.

Changing the dryer took a couple minutes. Changing the valve took longer. As it was explained to me, the expansion valve and drier are to be replaced every couple years, depending on use. I use my A/C a great deal.

A friend of a freind got me the parts. He only told me that the dryer was not hard to find, but the expansion valve took a little time. I think he said they use it on Jags and its from Germany. I paid $200 or so for both.

Good luck!